A microwave scanning surface harmonic microscope using a re-entrant resonant cavity

We report on a microwave scanning surface harmonic microscope obtained by inserting a tube scanning microscope into a re-entrant resonant cavity. We have chosen a re-entrant cavity for its easy design, for the relatively high loaded Q (>1500), and for the possibility of localizing the electric field within a well-defined and small region. The high value of the RF electric field, present between the tip and the sample, can generate harmonic currents which excite the resonant mode of the cavity. The nonlinear current signal, when properly elaborated, can give information on surface parameters of scientific and technological interest. In particular the instrument seems appropriate for studying the semiconductor-oxide interface behaviour and for the study of the properties of thin films of molecules such as Langmuir-Blodgett films. Preliminary results show that the instrument can image, with sub-nanometric resolution, conducting and oxidized surfaces.